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Beautiful but doomed: Demise of the passenger pigeon

Extinction was not down to the birds’ stupidity or frailty (Image&colon; Marc Schlossman/Panos)

Hubristic humans should heed the tale of the passenger pigeon’s demise, recounted by three books published on the centenary of its extinction

THIS September marks a melancholy anniversary&colon; the first of the month is the centennial of the death of Martha the pigeon in Cincinnati zoo and, with her passing, the extinction of the passenger pigeon. It was an extinction that 100 years earlier would have been inconceivable.

This was a species that moved in flocks of billions of individuals, so dense as to blot out the sun and take days to pass. Birds pausing on trees did so in numbers sufficient to break the boughs under their weight. Luckily, while they fed on a wide variety of fruits and seeds, passenger pigeons preferred mass-fruiting species such as chestnut, whose branches were large, dense and fecund enough to support the enormous numbers.

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Passenger pigeons moved in flocks of billions, so dense as to blot out the sun and take days to pass

They were superbly adapted to long-distance flying, and ranged over much of eastern North America, moving in a perpetual search for food. The pause for reproduction was brief, annual and occurred in colonies that covered thousands of hectares.

The passenger pigeon was among the most abundant bird species that ever lived. Yet a combination of trapping, shooting and collecting young birds to eat, plus the destruction of its habitat, occurred on such a massive scale that eventually Martha was all that was left. And then she was gone.

The anniversary has been marked by the publication of three very different books, all focusing on how a species can go from sky-darkening abundance to a single, aged individual in a matter of decades – and what this may tell us about the future.

The most visually beautiful is Errol Fuller’s The Passenger Pigeon, which gives a fine account of the species, its biology and its demise. We also learn what a superb long-distance flying machine this bird was, with huge flight muscles, greatly enlarged shoulder bones and sternum for endurance, and a tapering, highly aerodynamic shape and falcon-like wings for speed. As Fuller emphasises, this was no dodderer, extinct because it was too stupid or frail to survive.

Instead, as Joel Greenberg shows in A Feathered River Across the Sky, it was habitat destruction that largely did for the species. Accustomed to peregrinations in search of patchy and ephemeral resources, passenger pigeons simply couldn’t adapt to the newly deforested, industrialising landscape of 19th-century North America. This, plus the odd fact that pigeons left fattened, ground-foraging young to fend for themselves for the last two weeks before they could fly, ultimately led to their disappearance.

In A Message from Martha, Mark Avery, who was formerly conservation director of the Royal Society for the Protection of Birds, puts passenger pigeon biology in context by comparisons with great migrators such as the Manx shearwater and the albatross. He then provides a detailed analysis of how humans caused an inevitable decline.

So what can we learn from the demise of the passenger pigeon? The take-home message must be that of the tipping point, the moment beyond which movement to a new stable state is the only option. As the species adapted, psychologically and biologically, to only breed in large crowds, it was doomed once its population fell below a critical threshold.

As seas acidify, glaciers melt and forest cover fragments, I can’t help wondering how many Marthas humanity is pushing towards non-recoverable change. And whether we, the most abundant primate that ever lived, may one day, equally unexpectedly, share her fate.